Ultraviolet rays included in sunlight reaching the ground adversely affect the human body such as the skin, buildings such as houses, and the like so that various countermeasures for shielding ultraviolet rays have been proposed. While ultraviolet rays are divided into A region (wavelength of 320 to 380 nm) and B region (wavelength of 290 to 320 nm) according to Commission Internationale de l'Eclairage (CIE), it is of great concern that the amount of ultraviolet rays reaching the ground have recently been increasing with the decomposition of the ozonosphere by flon and the like. Furthermore, while the conventional target of shielding ultraviolet rays has been confined to B region, it has recently been revealed that the ultraviolet rays of A region penetrates deep into the skin to damage the tissue and accelerate skin aging. Therefore, not only B region but also A region have been attracting attention as a target of shielding ultraviolet rays.
Ultraviolet rays-absorbing compositions conventionally used in cosmetic sunscreens, ultraviolet rays-shielding coatings and the like mainly comprise organic compounds, such as benzophenone compounds, benzoic acid derivatives or the like. Since these organic compounds show absorption bands generally in the range of from 280 to 350 nm, the ultraviolet rays of A region cannot be completely shielded.
Additionally ultraviolet rays-absorbing compositions comprising organic compounds are problematical from the standpoint of safety to the human body.
Inorganic pigments showing broader ultraviolet rays-absorption bands have also been used in place of the organic compounds. In particular, a cosmetic composition or a coating composition containing ultrafine particles having an average primary particle size of 0.1 .mu.m or less forms a translucent coating film with a natural tone. Of these inorganic pigments, titanium oxide has enjoyed the most frequent use because it completely shields ultraviolet rays having a wavelength of 360 nm or shorter.
In recent years, zinc oxide has attracted attention as disclosed in JP-B-7-23294. Zinc oxide exhibits a still broader ultraviolet rays-absorption band than titanium oxide and completely shields ultraviolet rays having a wavelength of 370 nm or shorter. Furthermore, the hiding power of zinc oxide is not so high because of its low refractive index ranging from 1.9 to 2.0, so that it gives excellent translucence free from white turbidity when made into ultrafine particles of 0.1 .mu.m or smaller. For use in a coating composition, it can easily be colored. For use in cosmetics, zinc oxide can provide the composition with astringency or an antiinflammatory effect and also has a sebum absorbing effect.
Cerium oxide is known to have an ultraviolet rays-absorbing effect similarly to zinc oxide and titanium oxide. Although cerium oxide does not show a clear absorption end unlike zinc oxide or titanium oxide, it has a still broader absorption band than zinc oxide and titanium oxide and shields ultraviolet rays of 380 nm or shorter. Accordingly, cerium oxide can be used for its ultraviolet rays-absorbing effect similarly to zinc oxide and titanium oxide.
If ultrafine particles of zinc oxide, cerium oxide or titanium oxide are used as a component of cosmetics or coatings, they must be uniformly dispersed in a medium. However, ultrafine particles having a particle size, e.g., of 0.1 .mu.m or smaller readily undergo secondary agglomeration due to their great van der Waals forces. It is difficult to uniformly disperse the coarse secondary particles. Cosmetics, for instance, containing the particles in a non-uniformly dispersed state cannot get rid of color unevenness or an uncomfortable feel to the touch when applied to the skin.
In the field of pigments, pearlescent pigments which not only have a plurality of hues but vary their hue depending on the view angle have been extending their use in cosmetics and the like with the increasing diversity of liking. Pearlescent pigments are prepared by coating plate particles obtained by grinding naturally occurring substances, such as talc, mica, sericite and the like, with metal oxides, such as titanium dioxide, silica, alumina, zirconium oxide, iron oxide and the like.
Various improvements have been added to such pearlescent pigments. For example, JP-A-5-23671 discloses a technique of obtaining an oil-repellent pearlescent pigment which comprises coating mica flakes with titanium dioxide and further treating the surface of the coated flakes with a perfluoroalkylsilane.
JP-A-2-179954 discloses a technique of obtaining a weatherable pearlescent pigment comprising mica flakes having a coat of a solid solution of nickel oxide, cobalt oxide and the like as a color forming material when mica flakes are coated with titanium dioxide.
JP-A-5-17329 proposes a technique of obtaining a highly ultraviolet rays-shielding pearlescent pigment comprising sericite particles having a titanium oxide coat which is further coated with zinc oxide.
Thus, a number of improvements on pearlescent pigments have so far been made, but the techniques using plate particles obtained by grinding naturally occurring materials, such as talc, mica, sericite and the like, as a substrate are unavoidably disadvantageous in that the substrate particles have unevenness in color due to impurities, which results in unevenness in tone of final products. This has made product color control difficult particularly for those products putting weight on color, such as cosmetics.
Furthermore, because they are natural substances, it is difficult to secure a requisite quantity of a substance with stable properties. In particular, sericite has become hardly available. Mica is relatively easy to get, but its cleavage makes it difficult to secure a constant shape as flaky powder.
Hence, it has been proposed to apply flaky powder of barium sulfate which is easy to synthesize to cosmetics.
JP-B-62-34688 discloses a process for producing plate barium sulfate particles regular in size which comprises reacting barium sulfide and sulfuric acid at a molar ratio of 1:1. However, this process provides coarse barium sulfate particles, which are suitable for use as an additive to synthetic resins but are not always satisfactory for use in cosmetics.
JP-B-49-46908 discloses a technique in which a flaky pigment comprising fine plate crystals of barium sulfate having a thin coating film of titanium oxide, zirconium oxide, zinc oxide and the like is used as a component of make-up cosmetics. According to the disclosure, the flaky pigment exhibits a luster and a satisfactory feel to the touch as well as spreadability. However, the term "luster" as used therein is intended to mean the property of allowing the pigment deposited and bound for imparting a color to appear clearly, which is different from a so-called pearly luster.
Based on the above circumstances, an object of the invention is to provide a ultraviolet rays-absorbing composition having constant quality in terms of hue and pearly luster and provides satisfactory translucence and a satisfactory feel. Another object of the invention is to provide a process for producing the composition.